1. Field of the Invention
The present invention relates to the field of Personal Computer Memory Card International Association (PCMCIA) PC cards. Specifically, the present invention relates to an apparatus and method for sequencing control signals and removing and applying power to circuitry within a PC card so as to reduce power consumption and, thus, prolong battery life for a portable computer system or electronic device in to which the PC card is plugged.
2. Description of Related Art
The Personal Computer Memory Card International Association (PCMCIA) defines and promulgates standards for data storage and peripheral expansion (I/O) cards for computer systems and other electronic products. One such standard is referred to as the PC card standard and governs an I/O type card known as a PC card. The standard is based on an integrated circuit card having 68 pins which can be plugged into a socket, or slot of a computer system or other electronic device, hereinafter referred to as a host system, that adheres to the electrical, physical and software requirements set forth in the standard. Today, credit card-sized peripheral devices, such as fax modems and network adapters, adhering to the PC card standard, are commercially available.
Currently, the worldwide market for portable computer systems and electronic devices, such as, but not limited to, notebooks, subnotebooks, palmtop computer systems and personal digital assistants is, overall, growing rapidly. Concomitant with the market growth for such systems is the demand for supported peripheral devices. Given the physical dimensions of these portable electronic systems, the dimensions and weight of peripheral devices supported by such systems become a critically important factor. Thus, credit-card sized peripheral devices (54 mm.times.85.6 mm.times.3.3/5.0 mm) compliant with the PC card standard are commonly supported by these systems.
Another important factor in portable computer systems and electronic devices is battery life, that is, the number of hours such systems can operate under battery power before recharging or replacing batteries. For example, battery life for a personal computer (PC) notebook is currently on the order of four to five hours. A number of factors, such as the use of low voltage (e.g., 3.3 volts) circuitry and the improvement in battery technology have helped extend battery life. Another way to further prolong battery life is to allow portable computer systems to shut down, that is, remove power from, circuitry not in use, including a PC card plugged in to and drawing power from the portable computer system.
Presently, the only method of significantly reducing power consumption with respect to a PC card involves powering down the entire PC card. No attempt is made to save information, such as current configuration settings, stored within the PC card to nonvolatile storage residing within the host system or the PC card before the PC card is powered down. As a result, the PC card must be loaded with default settings upon later power up. Any current configuration settings or data present in the PC card at the time of power down is irretrievably lost.
Furthermore, upon power down of the PC card, no attempt is made to sequence control signals to or removal of power from devices or circuitry within the PC card to prevent a possible so-called CMOS latchup condition. A CMOS latchup condition can occur when voltage is allowed to repeatedly exceed a maximum withstandable level, permanently damaging CMOS circuitry present within the PC card.
Likewise, upon power up of the PC card, no attempt is made to properly sequence control signals or the application of power to devices or circuitry within the PC card to prevent CMOS latchup or stabilize any oscillators present within the PC card.
Thus, a better apparatus and method for powering down a PC card, one that sequences control signals and removal of power in a way that protects the circuitry located therein, and provides an option to save information contained therein, is needed.